RESUMO
AMPK is a conserved serine/threonine kinase whose activity maintains cellular energy homeostasis. Eukaryotic AMPK exists as αßγ complexes, whose regulatory γ subunit confers energy sensor function by binding adenine nucleotides. Humans bearing activating mutations in the γ2 subunit exhibit a phenotype including unexplained slowing of heart rate (bradycardia). Here, we show that γ2 AMPK activation downregulates fundamental sinoatrial cell pacemaker mechanisms to lower heart rate, including sarcolemmal hyperpolarization-activated current (I f) and ryanodine receptor-derived diastolic local subsarcolemmal Ca2+ release. In contrast, loss of γ2 AMPK induces a reciprocal phenotype of increased heart rate, and prevents the adaptive intrinsic bradycardia of endurance training. Our results reveal that in mammals, for which heart rate is a key determinant of cardiac energy demand, AMPK functions in an organ-specific manner to maintain cardiac energy homeostasis and determines cardiac physiological adaptation to exercise by modulating intrinsic sinoatrial cell behavior.
Assuntos
Proteínas Quinases Ativadas por AMP/genética , Bradicardia/genética , Cálcio/metabolismo , Frequência Cardíaca/genética , Sarcolema/metabolismo , Nó Sinoatrial/metabolismo , Adulto , Animais , Bradicardia/metabolismo , Eletrocardiografia Ambulatorial , Exercício Físico , Coração/diagnóstico por imagem , Humanos , Imagem Cinética por Ressonância Magnética , Espectroscopia de Ressonância Magnética , Camundongos , Microscopia Eletrônica de Transmissão , Mutação , Miocárdio/metabolismo , Miocárdio/patologia , Miocárdio/ultraestrutura , Condicionamento Físico Animal , Resistência Física , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Nó Sinoatrial/patologiaRESUMO
Treatment of the "sick sinus syndrome" is based on artificial pacemakers. These bear hazards such as battery failure and infections. Moreover, they lack hormone responsiveness and the overall procedure is cost-intensive. "Biological pacemakers" generated from PSCs may become an alternative, yet the typical content of pacemaker cells in Embryoid Bodies (EBs) is extremely low. The described protocol combines "forward programming" of murine PSCs via the sinus node inducer TBX3 with Myh6-promoter based antibiotic selection. This yields cardiomyocyte aggregates consistent of >80% physiologically functional pacemaker cells. These "induced-sinoatrial-bodies" ("iSABs") are spontaneously contracting at yet unreached frequencies (400-500 bpm) corresponding to nodal cells isolated from mouse hearts and are able to pace murine myocardium ex vivo. Using the described protocol highly pure sinus nodal single cells can be generated which e.g. can be used for in vitro drug testing. Furthermore, the iSABs generated according to this protocol may become a crucial step towards heart tissue engineering.